View interpolation consists in interpolating a disparity map for the new view, and then in synthesizing the view by interpolating video information using this interpolated disparity map and the left or right views.
Aliasing will appear in the interpolated disparity map. During the view synthesis, the picture information is interpolated using this interpolated disparity map with this aliasing. This introduces aliasing in the projected view.
This problem occurs because the common disparity map format defines only one disparity value per pixel. As a result for a pixel lying on an object border this value can either be the disparity value of the background object or the disparity value of the foreground object. This means that in the disparity map objects have aliased borders. Since this disparity map is used to render the synthesized view, the synthesized view will also show aliased object borders.
A disparity map represents for each pixel the disparity between the left and the right frames or pictures. A depth map represents for each pixel the depth of the corresponding object in the 3D scene. The invention will be described using a disparity map but is exactly the same if using a depth map.
However on object borders for some pixels there is background and foreground video information. But since in the disparity (resp. depth) map only one disparity value per pixel can be stored, this value cannot be exactly correct. For a pixel on the object border this value can either be the disparity value of the background object, the disparity value of the foreground object, or a value in between.
As a result object borders in the disparity map can only be located at pixel borders. This means that in the disparity map object borders exhibit aliasing.
Document D1 (Boundary matting for view synthesis from S. Hasinoff) proposes a method called boundary matting to reduce the “cut-out” appearance. This method exploits multiviews to perform alpha matting and to refine stereo depths at the boundaries with sub-pixel accuracy. The method aims at defining precise object boundaries using the picture information and relies on quite complex matting techniques.
Document D2 (U.S. Pat. No. 6,577,307) discloses an anti aliasing process for 3D graphic rendering. The method retrieves the depth of two nearest polygons, and stores the corresponding color information and a weighing value indicating the percentage of coverage of a pixel. This weighting value is used to blend the foreground and background colors. The object boundaries and the percentage of coverage of a pixel depend only on the position of the polygons which are perfectly known. This method cannot be used in case of view synthesis since the exact object border shapes are not known.